Fluid regulators are commonly used to reduce the pressure of a fluid and regulate the pressure to a substantially constant value. Specifically, a fluid regulator has an inlet that receives a supply fluid at a relatively high pressure and provides a relatively lower set control pressure at an outlet. Inlet pressure is reduced to a lower outlet pressure by restricting flow through an orifice to substantially match the fluctuating downstream demand. For example, a gas regulator associated with a piece of equipment (e.g., a boiler) may receive a gas having a relatively high and somewhat variable pressure from a gas distribution source and may regulate the gas to have a lower, substantially constant or control pressure suitable for safe, efficient use by the equipment.
Fluid regulators are often classified based on the ability of the fluid regulator to maintain an outlet pressure at a set control pressure when the fluid regulator is exposed to a range of pressure differentials. A fluid regulator that deviates an unacceptable amount from the set control pressure when the fluid regulator is exposed to a particular pressure differential is deemed to be outside the classification or accuracy class of the regulator. Deviation from the set control pressure is often caused by droop and/or boost flow characteristics of the fluid regulator. Boost flow characteristics can significantly degrade the accuracy and/or capacity classification of a fluid regulator.